Electron tube coating



Sept. 30, 1947.

M. ORLOVE ELECTRON TUBE COATING Filed Nov. '7, 1942 (Co op er 525 A 2%278/2 [a m 2 m: .V mm IR 0 Mm. w r a .ayw. M 0 e at. 60 Z r 6d m 3 6 a w e Patented Sept. 30, 1947 ELECTRON TUBE COATING Max Orlove, New York, N. Y., assignor of onehalf to Charles Schiffman, New York, N. Y.

Application November 7, 1942, Serial No. 464,841

7 Claims. 1

This invention relates to an electron tube coating.

The main object of the invention is to provide an electron-emissive coating which is capable of producing an exceedingly copious electronflow upon the application of a mild heat such, for example, as that generated in or by an electric glow discharge.

Another object of the invention is to provide a coating of the character described which requires very little current to produce a, copious electron flow so that the power efficiency of a tube containing such coating is very high,

Other objects of the invention will in part be obvious and in part hereinafter pointed out.

Certain features of the invention describedbut not claimed herein are shown, described, and claimed in my copending application Serial No. 464,840, for Electronic tubes, filed on the 7th day of November, 1942.

In the accompanying drawings, in which are shown various possible embodiments of the invention,

Fig. 1 is an enlarged fragmentary perspective Fig. 1a is an enlarged fragmentary sectional view of the envelope of an electronic tube Whose inner surface is covered with a coating embodying amodified form of my invention; and

Figs. 2, 3 and 4 are broken away isometric views of electronic tubes to Which coatings embodying my invention have been variously applied.

Heretofore electron-emissive coatings in electronic tubes have been energized either by light or a similar form of energy, or by heat. Where light or similar energy was employed, it has been difficult to produce a copious flow of electrons under such mild stimulation and to energize large surfaces without unduly complicating and enlarging the tube construction. On the other hand, where heretofore, heat was employed for energization, it was necessary to use high temperatures which could only be produced by heating filaments to incandescence. Such filaments, however, were very fragile and the current flowing therethrough and electron-emission there from interfered with the space charge of the electronic tube and the release of electrons from the filament or a surface coated with an electronemissive substance.

In accordance with the present invention, I

copious flow of electrons at mild temperatures so that an electronic tube embodying my coating can be of simple construction; light weight, and rug ed design, and capable, therefore, of efiicient use under trying conditions in tanks; ships and airplanes.

Referring now-to the drawings andmore particularly to Fig. 1, I have there shown a fragment In of an electronic tube envelope on-which there is disposed, in accordance with m-y'invention, a coating comprising at=least two layers which, for conveniencawill be denominated, the base layer 12 (next to the surface of the member It being coated) and the emissive layer l4; (exposed to the. interior of the electronic tube). Ordinarily, the tube after being provided with the coating and suitable electrodes is evacuatedrand sealed.

The base layer l2, whichmay berapplied toany desired portion of the interior surface of the electronic tube, comprises. two-substances having different. thermoelectric potentials; Said sub.- stances are in finally subdivided form and are uniformly dispersed. and intimately mixed throughout said layer and hcld'to-the tube surface by a suitable binder well-known to this art. The base layer may be prepared by pulverizing or powdering the two substances to be employed, mixing them in the proper proportions, and adding to them a suitable binder and ahighly volatile solvent. Th composite fluid may then be 7 applied to the surface-in a-suitablemanner, as

haveprovided'a novel coating which will emit a by spraying or brushing. Upon evaporation of' the solvent the base layer will adhere to the tube surface. I preferably. employ a thin base layer and obtain the same by using a relatively large percentage of the highly volatile solvent.

One of the two substances in thebase layer is copper oxide and the other selenium. A mixture of 50% by weight of'selenium and-50% by weight of copper'oxide, to which has been added a minimum amount of binderand a-suitable quantity of solvent, will provide a base layer from which highly desirable results areobtained. Desirable results are also obtainedwhere thepercentage by weight of selenium varies from 40% to and that of copper oxide varies; from 60% to 40%. However, results which constitute: a marked improvement over the coatings. heretofore employed in the art are obtainedwhen the percentage of copper oxide is as low as 01.5% or is as high as 99.5% by weight and the percentage by weight of selenium correspondingly varies from. 99.5% to 0.5%.

It will be understood from. the. foregoing that the term substance embraces individual compounds, i. e., that a compound, e. g. copper oxide, is but a single substance as this term is used in the specification and claims.

The emissive layer I4 is applied to the base layer [2 after the latter is thoroughly dry and is composed of finely subdivided well-known substances which emit electrons at elevated temperatures. Such substances may be selected from the group consisting of barium oxide, strontium oxide, caesium oxide and thorium oxide. Various mixtures of these substances can be used.

To this mixture is added a minimum amount of binder and a-suitable quantity of a highly volatile solvent.

I can also, if desired, apply the emissive layer in the form of a deposit of carbonates rather than oxides of the above metals and activate such layers by heating in any well-known manner the coating to drive off the carbon dioxide.

Still another method of applying the emissive layer is to deposit a pellet in the tube to be coated, which pellet comprises in proper proportions carbonates of the metals desired to be used. The pellet can be raised to a high temperature whereupon its constituent carbonate compounds will be transformed to oxides and deposited upon the walls of the tube.

A typical example of a carbonate mixture is Example Per cent by weight Caesium carbonate Between 33 /3 and 50 Barium carbonate 2 Strontium carbonate Between 66 /3 and 50 To this may be added from 5% to 8% but not more than 10% by weight of calcium nitrate so that the complete mixture is 100% of carbonates plus an additional 5% to 10% of calcium nitrate. If sprayed a binder and volatile solvent are also added.

I have found that when mild temperatures are applied to an electronic tube having a two-layered coating, such'as described, an exceedingly copious flow of electrons is emitted therefrom. For example, when the temperature of the coating is raised to that of the human body, an appreciable flow of the electrons results. However, I prefer to energize the coating by applying a higher temperature. This may be accomplished by subjecting the coating to the heat generated in or by an electric glow discharge, such as for example that of a positive column electric discharge lamp. A tube having a coating such as described herein, and energized in this manner is fully illustrated and described in my said copending application. Such heat energization may be carried out by coating the interior of a glass envelope with the said two layers and then so positioning the envelope that a'portion thereof is exposed to the electron now in a positive column electric discharge lamp. The heat generated by the lamp and by bombardment of the electronic stream on the tube envelope sufiices to energize my novel coating to a high degree and it will be found that with such energization, an exceedingly copious stream of electrons is emitted. This stream is far greater than that which would be emitted if the emissive layer alone were raised to the same degree of temperature.

The flow of electrons is so copious that the electronic tube need not even be evacuated. However, in such case, oxygen which would deteriorate the coating, should be removed. This. can be accomplished in any way known to the prior art, as for example, gettering.

An electronic tube containing my novel coating has one or more electrodes according to the type of circuit in which the tube is to be used. Thus, a tube I5 (Fig. 2), used as a rectifier, may have one metal electrode I8 to act as an anode, while the coating 20 serves as a cathode. If the coating is to be employed in this manner, it is preferable to dispose a layer 22 (see also Fig. la) of an electrically conductive substance, such as copper, between the base layer 24 and the interior surface 26 of the tube or member on which the coating is supported. Said coating includes the usual layer 21 of electron-emissive substances superimposed on the base layer 24.

Alternatively, as explained in my said copending application, a tube 38 (Fig. 3), acting as a rectifier, can be providedwith two metallic electrodes 32, 34, one 32 of which serves as an-anode and the other 34 as a cathode. In such cases, it

is not necessary for any potential to be applied to the coating 36 and there need not be any conductive layer interposed between the base layer.

and the surface of the supporting member. I have found however, that the electron emission of my novel coating is considerably enhanced and takes place at a much more uniform rate when an electrically conductive layer is interposed between said base layer and said supporting memher, even when the coating is not to serve as an electrode. Accordingly, in the preferred form of my invention, I include such a third layer 38 as an element of the coating. Said third layer can be applied to the surface of the member to be coated in any manner known to the art, as for example by spraying or electro-deposition. I have found that when this layer is of copper, highly satisfactory results are obtained. However, other electrically conductive materials, as for example silver, can be employed. The material selected for the underlying electrically conductive layer should have a thermoelectric potential different from and preferably lower than the thermoelectric potential of the base layer.

As shown in Fig. 4 I may also place my coating 40 comprising the base layer 42 and the emissive layer 44 directly upon a metallic electrode 46 instead of upon a conductive layer.

I believe that the unusual activity of the emissive layer when subjected to the moderate or mild temperatures above described is due mainly to the presence of the base layer and to some degree to the presence of the underlying electrically conductive layer. I believe that said base layer speeds up emission by generation of a potential on the surface adjacent the emissive layer. I do not however, wish to be limited to this theory of operation.

It will thus be seen that I have provided an improved electron-emissive coating which achieves the several objects of this invention and which ishaving thereon an electron-emissive coating comprising a base layer on said member and an electron-emissive layer on said base layer, said base layer consisting essentially of an intimate, uniform physical mixture of copper oxide and selenium and said electron-emissive layer including an electron-emissive substance selected from the group consisting of the oxides of barium, strontium, caesium, and thorium.

2. An electronic tube including a member with a surface at the inside of the tube, said surface having thereon an electron-emissive coating comprising a base layer on said member and an electron-emissive layer on said base layer, said base yer consisting essentially of an intimate, uniform physical mixture of copper oxide and selenium and said electron-emissive layer including an electron-emissive substance selected from the group consisting of the oxides of barium, strontium, caesium and thorium, and a layer of an electrically conductive material intermediate said base layer and said member.

3. An electronic tube including a member with a surface at the inside of the tube, said surface having thereon an electron-emissive coating comprising a base layer on said member and an electron-emissive layer on said base layer, said layer consisting essentially of an intimate, uniform physical mixture of copper oxide and selenium particles and said electron-emissive layer including an electron-emissive substance selected from the group consisting of the oxides of barium, strontium, caesium and thorium, and a layer of a metal selected from the group consisting of copper and silver interposed between said base layer and said member.

4. An electronic tube including a member with a surface at the inside of the tube, said surface having thereon an electron-emissive coating comprising a base layer on said member and an electronic-emissive member on said base layer, said base layer consisting essentially of an intimate, uniform physical mixture of from about 0.5% to about 99.5%, by weight, of selenium and from about 99.5% to about 0.5%, by weight, of copper oxide, said electron-emissive layer including an electron-emissive substance selected from the group consisting of the oxides of barium, strontium, caesium and thorium.

5. An electronic tube including a member with a surface at the inside of the tube, said surface having thereon an electron-emissive coating comprising a base layer on said member and an electronic-emissive member on said base layer, said base layer consisting essentially of an intimate,

uniform physical mixture of from about 40% to about by weight, of selenium and from about 60% to about 40%, by Weight, of copper oxide, said electron-emissive layer including an electron-emissive substance selected from the group consisting of the oxides of barium, strontium, caesium and thorium.

6. An electronic tube including a member with a surface at the inside of the tube, said surface having thereon an electron-emissive coating comprising a base layer on said member and an electron-emissive member on said base layer, said base layer consisting essentially of an intimate, uniform physical mixture of 50%, by Weight, of selenium and 50%, by weight, of copper oxide, said electron-emissive layer including an electron-emissive substance selected from the group consisting of the oxides of barium, strontium, caesium and thorium.

7. An electronic tube including a, member with a surface at the inside of the tube, said surface having thereon an electron-emissive coating com- .prising a base layer on said member and an electronic-emissive member on said base layer, said base layer consisting essentially of an intimate, uniform physical mixture of 50%, by weight, of selenium and 50%, by Weight, of copper oxide, said electron-emissive layer including an electron-emissive substance selected from the group consisting of the oxides of barium, strontium, caesium and thorium, and a layer of copper intermediate said base layer and said member.

MAX ORLOVE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,718,123 Dobben et a1 June 18, 1929 2,123,024 Piore et a1 July 5, 1938 2,172,207 Kolligs et al Sept. 5, 1939 2,147,669 Piore Feb. 21, 1939 2,242,395 Hartmann et a1. May 20, 1941 2,210,683 Maurer Aug, 6, 1940 2,239,954 Fanselau Apr. 29, 1941 2,257,827 Weissenberg Oct. 7, 1941 2,003,344 De Boer et a1 June 4, 1935 2,065,947 Nauth Dec. 29, 1936 FOREIGN PATENTS Number Country Date 592,732 Germany Feb. 13, 1934 612,693 Germany May 2, 1935 

